Novel lubricant additives

ABSTRACT

Novel organic phenol-containing silicon compounds of the formula &lt;IMAGE&gt;   are disclosed. These compounds are suitable for use as lubricant additives.

This is a continuation of application Ser. No. 064,238 filed on Aug. 6, 1979, now abandoned.

The present invention relates to novel phenol-containing silanes, process for their manufacture, their use as additives in lubricants, and the lubricants stabilised therewith.

Different additives are normally added to mineral and synthetic lubricants in order to improve their performance properties. In particular there is a need for additives which protect lubricant from attack by atmospheric oxygen and thereby prolong their life. The inhibition of oxidation is also advantageous as regards corrosion, as the formation of acid oxidation products is substantially prevented.

The present invention is based on the observation that a very good antioxidising and anticorrosive effect can be obtained in lubricants by the addition of phenol-containing silanes.

The compounds of the invention have the formula I ##STR2## wherein one of R₁ and R₃ is hydrogen and the other is OH, each of R₂, R₄ and R₅ independently is C₁ -C₁₂ alkyl, C₅ -C₇ cycloalkyl, C₆ -C₁₀ aryl or C₇ -C₉ aralkyl, and R₄ and R₅ are also hydrogen, R₆ is C₁ -C₁₈ alkyl, each of m and n independently is an integer from 0 to 6, X is the direct bond, --O--, --S--, --N(R₇)--, --Q--R₈ -- or ##STR3## wherein R₇ represents hydrogen, C₁ -C₁₂ alkyl, phenyl or a group of the formula II ##STR4## wherein R₁, R₂, R₃, R₄, R₅ and m are as defined above, Q is --O-- or --NH--, R₈ represents a group of the formula III

    --CH.sub.2 --CH(OR.sub.10)--CH.sub.2 --O--                 (III)

wherein R₁₀ is hydrogen, C₁ -C₁₂ alkyl or a group of the formula IV ##STR5## wherein r is an integer from 0 to 6, R₁₁ is hydrogen, C₁ -C₁₂ alkyl, C₅ -C₇ cycloalkyl, C₆ -C₁₀ aryl or C₇ -C₉ aralkyl, and R₉ is --O--,--NH--, --OH.H₂ N--, --O--CH₂ CH₂ --S--, ##STR6## --O--R₈ --, or a group of the formula V ##STR7## wherein R₈, R₁₁ and r are as defined above, and R₁₂ is C₁ -C₁₈ alkyl, C₅ -C₇ cycloalkyl, C₆ -C₁₀ aryl, C₇ -C₉ aralkyl or a group of the formulae VI or VII

    --(C.sub.u H.sub.2u)--COOR.sub.10                          (VI)

or ##STR8## wherein u is an integer from 1 to 6 and R₁₀, R₁₁ and r are as defined above.

One of R₁ and R₃, preferably R₃, is OH and the other is hydrogen.

R₂, R₄, R₅ and R₁₁ as C₁ -C₁₂ alkyl are e.g. methyl, ethyl, isopropyl, sec-butyl, tert-butyl, tert-pentyl, n-hexyl, 1,1,3,3-tetramethylbutyl, n-nonyl or 1,1,3,3,5,5-hexamethylhexyl. R₂ contains preferably 1 to 8 carbon atoms and is in particular methyl or tert-butyl. R₄ and R₁₁ are preferably C₁ -C₄ alkyl and, in particular, tert-butyl. R₅ as alkyl contains in particular 1 to 6 carbon atoms, but is preferably hydrogen.

Cycloalkyl represented by R₂, R₄, R₅, R₁₁ and R₁₂ is e.g. cyclopentyl, xcyclohexyl or cycloheptyl.

R₂, R₄, R₅, R₁₁ and R₁₂ as C₆ -C₁₀ aryl are e.g. phenyl, α- or β-naphthyl.

R₂, R₄, R₅, R₁₁ and R₁₂ as C₇ -C₉ aryl can be e.g. benzyl, α-phenylethyl or α,α-dimethylbenzyl.

R₆ and R₁₂ as C₁ -C₁₈ alkyl are e.g. methyl, ethyl, n-propyl, isopropyl, n-butyl, n-hexyl, n-octyl, 2-ethylhexyl, n-nonyl, n-dodecyl or n-octadecyl. In particular, R₆ is methyl or ethyl.

m has a value from 0 to 6, preferably from 0 to 4 and in particular from 1 to 3. n can be an integer from 0 to 6, but is preferably 3.

R₇ and R₁₀ as C₁ -C₁₂ alkyl are e.g. methyl, ethyl, isopropyl, n-propyl, n-butyl, sec-butyl, tert-butyl, n-pentyl, n-hexyl, n-octyl, 2-ethylhexyl, n-nonyl or n-dodecyl. R₁₀ preferbly contains 1 to 4 carbon atoms.

In addition to hydrogen, R₇ preferably also represents the group of the formula II, wherein m, R₁, R₂, R₃, R₄ and R₅ have the given meanings.

Q is --O-- and, in particular, --NH--, and r can be integer from 0 to 6, especially from 0 to 4, and is preferably 2.

The preferred meanings of R₉ are in particular --NH--, --O--CH₂ CH₂ --S-- and --OR₈ --. However, compounds in which R₉ is --OH.H₂ N-- are also of interest.

If X is the direct bond, the value of m is preferably 0 and that of n is preferably 2 or 3.

Interesting compounds are those of the formula I wherein R₁ is hydrogen, R₃ is OH and each of R₂, R₄ and R₆ independently is C₁ -C₁₂ alkyl and R₄ is also hydrogen, R₅ is hydrogen or C₁ -C₆ alkyl, m is an integer from 0 to 4 and n is 3, X is the direct bond, --O--, --S--, --N(R₇)--, --Q--R₈ -- or ##STR9## wherein R₇ is hydrogen or a group of the formula II, in which R₁, R₂, R₃, R₄, R₅ and m are as defined above, Q is --O-- or --NH--, R₈ is a group of the formula III, wherein R₁₀ is hydrogen, C₁ -C₁₂ alkyl or a group of the formula IV, wherein r is an integer from 0 to 4, R₁₁ is C₁ -C₁₂ alkyl, and R₉ is --O--, --NH--, --OH.H₂ N--, --O--CH₂ CH₂ --S--, --OR₈ -- or a group of the formula V, wherein R₈, r and R₁₁ have the above meanings.

Preferred compounds are those of the formula I wherein R₁ R₆ is methyl or ethyl, m is an integer from 0 to 4 and n is 3, X is the direct bond, --O--, --S--, --N(R₇)-- or ##STR10## wherein R₇ is a group of the formula II, in which R₁, R₂, R₃, R₅ and m are as defined above, R₉ is --NH--, --O--CH₂ --CH₂ --S-- or --OR₈ --, wherein R₈ is a group of the formula III, in which R₁₀ is hydrogen or a group of the formula IV, wherein r is 2 and R₁₁ is C₁ -C₄ alkyl.

Particularly preferred compounds are those of the formula I, wherein R₁ and R₅ are hydrogen, R₃ is OH, R₂ is methyl or tert-butyl, R₄ is tert-butyl, R₆ is methyl or ethyl, m is an integer from 1 to 3 and n is 3, X is the direct bond, --O--, --S--, --N(R₇)-- or ##STR11## wherein R₇ is a group of the formula II, in which R₁, R₂, R₃, R₄, R₅ and m have the above meanings, R₉ is --NH-- or --OR₈, wherein R₈ is a group of the formula III, in which R₁₀ is hydrogen.

Interesting compounds are also those of the formula I, wherein X is --NH--R₈ -- or ##STR12## in which R₈ is as defined above and R₉ is --OH.H₂ N--.

Examples of compounds of the formula I are:

    __________________________________________________________________________     (A)                                                                                ##STR13##                                                                  (1)                                                                               Y: S                          R.sub.6 : CH.sub.3                                                                   m:1                                     (2)                                                                               Y: OCH.sub.2CH(OH)CH.sub.2O   R.sub.6 : CH.sub.3                                                                   m:1                                     (3)                                                                                ##STR14##                    R.sub.6 : C.sub.2 H.sub.5                                                            m:1                                     (4)                                                                               Y: C(O)NH                     R.sub.6 : C.sub.2 H.sub.5                                                            m:2                                     (5)                                                                               Y: COOH.H.sub.2 N             R.sub.6 : C.sub.2 H.sub.5                                                            m:2                                     (6)                                                                               Y:                            R.sub.6 : CH.sub.3                                                                   m:2                                     (7)                                                                               Y: COOCH.sub.2CH(OH)CH.sub.2O R.sub.6 : CH.sub.3                                                                   m:2                                     (8)                                                                                ##STR15##                    R.sub.6 : CH.sub.3                                                                   m:2                                     (9)                                                                               Y: COOCH.sub.2CH.sub.2S       R.sub.6 : CH.sub.3                                                                   m:2                                     (10)                                                                               ##STR16##                    R.sub.6 : CH.sub.3                                                                   m:2                                     (11)                                                                               ##STR17##                    R.sub.6 : CH.sub.3                                                                   m:2                                     (12)                                                                              Y: NHCH.sub.2CH(OH)CH.sub.2O  R.sub.6 : CH.sub.3                                                                   m:0                                     (13)                                                                              Y: S                          R.sub.6 : CH.sub.3                                                                   m:3                                     (B)                                                                                ##STR18##                                                                  (C)                                                                                ##STR19##                                                                  (D)                                                                                ##STR20##                                                                  (1)                                                                               n:2                                                                         (2)                                                                               n:3                                                                         __________________________________________________________________________

The compounds of the formula I are obtained by known methods, for example by Michael addition or esterification or transesterification reactions. All reactions described hereinafter are preferably carried out under nitrogen.

The compounds of the formula I, wherein X is the direct bond, can be obtained e.g. by the reaction of a silane of the formula VIII

    HSi--OR.sub.6).sub.3                                       (VIII)

with a compound of the formula IX

    Z--(C.sub.m* H.sub.2m*)CH═CH.sub.2                     (XI)

wherein Z is a group of the formula X ##STR21## in the presence of a catalyst, such as hexachloroplatinic acid, preferably in a solvent, for example an alcohol, such as isopropanol.

In the formulae VIII, IX and X, the substituents R₁, R₂, R₃, R₄, R₅ and R₆ have the meanings given above and m* is an integer from 0 to 4.

A compound of the formula I, in which X is --O-- or --S--, is for example the reaction product of a mercaptan of the formula XI

    HS--(C.sub.n H.sub.2n)--SI--(--OR.sub.6).sub.3             (XI)

and a compound of the formula IX, preferably in the presence of a radical initiator, such as azoisobutyronitrile and a solvent, such as tetrahydrofurane. Compounds of the formula I, wherein m is 1, are most simply obtained by benzylation of a compound of the formula XI with a benzylating agent of the formula XII

    Z--R.sub.13                                                (XII)

wherein Z is a group of the formula (X) as defined above, and R₁₃ is hydrogen or --CH₂ Cl, --CH₂ NR₁₄ R₁₅ or --CH--S--C(S)--NR₁₄ R₁₅, wherein R₁₄ and R₁₅ are alkyl or together with the nitrogen atom to which they are attached form a 5- or 6-membered ring. When R₁₃ is hydrogen, the known benzylation is carried out in the presence of formaldehyde and an acid. In the formulae X, XI and XII, the symbols n, Z, R₁, R₂, R₃, R₄, R₅ and R₆ have the given meanings. Reactions of this type are described e.g. in U.S. Pat. No. 3,281,334.

Compounds of the formula I, wherein X is --N(R₇)--, can be obtained in known manner by reacting an amine of the formula XIII

    HN(R.sub.7)--C.sub.n H.sub.2n)Si--(--OR.sub.6).sub.3       (XIII)

with an aldehyde of the formula XIV

    Z--(C.sub.m** H.sub.2m**)CHO                               (XIV)

in the presence of a reduction system, such as H₂ /Pd. If R₇ in formula (XIII) is a group of the formula II, these compounds can be obtained e.g. from amines of the formula (XIII), wherein R₇ is hydrogen, with a phenol of the formula (XII), wherein R₁₃ is hydrogen, in the presence of formaldehyde. In the formulae XIII, XIV and II, the symbols Z, R₆, R₇, m and n have the meanings given above. m** is 0 to 5.

If X is --O--R₈ -- in compounds of the formula I, these latter are obtained e.g. by the reaction of an epoxide of the formula XV ##STR22## with an alcohol or amine of the formula XVI

    Z--(C.sub.m H.sub.2m)QH                                    (XVI)

preferably in a solvent, such as benzene, toluene or xylene. In these formulae, m, n, Z, R₆ and Q are as defined previously.

The resulting compounds (in which X is --Q--R₈ and R₈ is a group of the formula III, in which R₁₀ is hydrogen) can be alkylated or esterified in known manner to produce analogous products in which R₁₀ is alkyl or a group of the formua IV, wherein all the symbols have the meanings given above.

Substitution of compounds of the formula XVII

    Z--(C.sub.m H.sub.2m)--COOH                                (XVII)

or those of the formula XVIII

    NaS--CH.sub.2 COOR.sub.12                                  (XVIII)

for the compounds of the formula XVI in the above reaction, in which case the reaction products obtained from compounds of the formulae XVI and XVIII are subsequently esterified in known manner with compounds of the formula XVII or the lower alkyl esters thereof, yields compounds of the formula I, wherein X is --C(O)--R₉ and R₉ is --O--R₈ -- or --O--CH(CH₂ --S--R₁₂)--CH₂ --O. Reaction of the hydroxy compound of the --O--R₈ -- type with a compound of the formula XVII or the lower alkyl ester thereof yields compounds of the formula I, wherein X is --C(O)--R₉ --, R₉ is --O--R₈ -- and R₈ is a group of the formula III, wherein R₁₀ is a group of the formula IV. Unless otherwise indicated, all the symbols referred to are as defined previously.

Compounds of the formula I, wherein X is --C(O)--R₉, and R₉ is --O-- or --O--CH₂ CH₂ --S-- are most simply obtained by reacting a chloride of the formula XIX

    (R.sub.6 O).sub.3 --Si--(--C.sub.n H.sub.2n)--Cl           (XIX)

with a compound of the formula XX

    Z--(C.sub.m H.sub.2m)COOR.sub.16                           (XX)

wherein R₁₆ is Na or --CH₂ CH₂ --SH, and the other symbols of the formulae XIX and XX have the given meanings.

The compounds of the formula I, wherein X is --C(O)--R₉ --, and R₉ is --NH-- or a group of the formula V, are obtained e.g. by reaction of an amine of the formula XXI

    R.sub.17 --NH--(C.sub.n H.sub.2n)--Si--(--OR.sub.6)        (XXI)

wherein R₁₇ is hydrogen or H₂ N--(CH₂)₂ --, with a lower alkyl ester of the acids of the formula XVII, in the presence of a basic catalyst, such as lithium amide, in an aprotic solvent such as benzene, toluene or xylene.

Compounds of the formula I, wherein X is --C(O)--R₉ -- and R₉ is --OH.H₂ N--, are obtained by reacting an amine of the formula XXI with a carboxylic acid of the formula XVII, without a catalyst in an aprotic solvent for example toluene or dioxane.

The starting materials of the formulae VIII to XXI employed for the known methods of manufacture described above are known or, if they are new, can be obtained in analogous manner. Many of these compounds are commercially available.

Even when used in very insignificant amounts, the compounds of the formula I act as stabilisers against oxidation and corrosion in lubricants. Accordingly, mineral and synthetic lubricating oils, as well as mixtures thereof, which contain 0.001 to 5 percent by weight, based on the lubricant, and preferably 0.02 to 3 percent by weight, of a compound of the formula I, exhibit excellent lubricating properties which become evident due to the greatly reduced signs of wear of the friction surface to be lubricated. The suitable lubricants are known to the skilled person and are described for example in the "Schmiermittel Taschenbuch" (Huthig Verlag, Heidelberg, 1974).

The lubricating oil formulation can contain still further additives which are added to improve certain performance properties, such as antioxidants, metal deactivators, rust inhibitors, viscosity index improvers, pour-point depressors, dispersant/surfactants and other wear resisting additives.

Examles of antioxidants are:

(a) Alkylated and non-alkylated aromatic amines and mixtures thereof, for example: dioctyldiphenylamine, 2,2,3,3-tetramethylbutylphenyl-α- and -β-naphthylamines, phenotriazine, dioctylphenothiazine, phenyl-α-naphthylamine, N,N'-di-sec-butyl-p-phenylenediamine.

(b) Sterically hindered phenols, for example: 2,6-di-tert-butyl-p-cresol, 4,4'-bis-(2,6-diisopropylphenol), 2,4,6-triisopropylphenol, 2,2'-thio-bis-(4-methyl-6-tert-butylphenol), 4,4'-methylene-bis-(2,6-di-tert-butylphenol).

(c) Alkyl-, aryl- or aralkylarylphosphites, for example: trinonylphosphite, triphenylphosphite, diphenyldecylphosphite.

(d) Esters of thiodipropionic acid or thiodiacetic acid, for example: dilaurylthiodipropionate or dioctylthiodiacetate.

(e) Salts of carbamic and dithiophosphoric acids, for example: antimony diamyldithiocarbamate, zinc diamyldithiophosphate.

(f) A combination of two or more of the above antioxidants, for example: an alkylated amine and a sterically hindered phenol.

Examples of metal deactivators are:

(a) for copper, e.g.: benzotriazole, tetrahydrobenzotriazole, 2-mercaptobenzotriazole, 2,5-dimercaptothiadiazole, salicylidene propylenediamine, salts of salicylaminoguanidine.

(b) for lead, e.g.: sebacid acid derivatives, quinizarine, propyl gallate.

(c) A combination of two or more of the above additives.

Examples of rust inhibitors are:

(a) Organic acids, the esters, metal salts and anhydrides thereof, e.g.: N-oleyl-sarcosine, sorbitan mono-oleate, lead naphthenate, dodecenylsuccinic anhydride.

(b) Nitrogen-containing compounds, for example:

I. Primary, secondary or tertiary aliphatic or cyclo-aliphatic amines and amine salts of organic and inorganic acids, for example, oil-soluble alkylammonium carboxylates.

II. Heterocyclic compounds, e.g. substituted imidazolines and oxazolines.

(c) Phosphorus-containing compounds, for example: amine salts of phosphoric acid partial esters.

(d) Sulfur-containing compounds, for example: barium dinonylnaphthalenesulfonates, calcium petroleum sulfonates.

(e) Combinations of two or more of the above additives.

Examples of Viscosity index improvers are:

polymethylacrylates, vinyl pyrrolidone/methacrylate copolymers, polybutene, olefin copolymers, styrene/acrylate copolymers.

Examples of pour-point depressors are:

polymethacrylates, alkylated naphthalene derivatives.

Examples of dispersants/surfactants are:

polybutenylsuccinic imides, polybutenylphosphonic acid derivatives, superbasic magnesium, calcium and barium sulfonates and phenolates.

Examples of wear resisting additives are:

compounds which contain sulfur and/or phosphorus and/or halogen, such as sulfurised vegetable oils, zinc dialkyldithiophosphates, tritolylphosphate, chlorinated paraffins, alkyl- and aryldisulfides.

The following Examples describe in closer detail the manufacture of the compounds to be employed as stabilisers in the lubricants according to the invention, and also the use and action of the lubricant compositions.

EXAMPLE 1

A solution of γ-aminopropyltriethoxysilane (22.1 g, 0.1 mole) in 50 ml if isopropanol is added dropwise in the course of 30 minutes to 40.6 g (0.2 mole) of 2,6-di-tert-butylphenol and 6 g (0.2 mole) of para-formaldehyde in 100 ml of isopropanol. The reaction mixture is kept for 16 hours at reflux temperature, then cooled and dried over sodium sulfate. The filtrate solvent is evaporated. The residue consists of 58.5 g of a clear orange oil having the following structure: ##STR23##

EXAMPLE 2

1 g of lithium amide is added at 80° C. under nitrogen to 29.2 g (0.1 mole) of methyl 4-hydroxy-3,5-di-tert-butylphenylpropionate and 22.1 g (0.1 mole) of γ-aminopropyltriethoxysilane in 150 ml of xylene. The temperature rises to 130°-135° C. in the course of 16 hours and the methanol formed is distilled off. The reaction mixture is diluted with about 300 ml of xylene, the lithium amide is neutralised with acetic acid, and the solvent is evaporated, affording 36.8 g of a dark oil having the following structure: ##STR24##

EXAMPLE 3

9.4 g (0.05 mole) of γ-aminopropyltriethoxysilane in 50 ml of toluene are added dropwise under nitrogen to 13.9 g (0.05 mole) of 4-hydroxy-3,5-di-tert-butylphenylpropionic acid in 100 ml of toluene. The reaction mixture is stirred for 16 hours at reflux temperature. The solvent is then evaporated, affording 20.3 g of a viscous oil having the structure: ##STR25##

EXAMPLE 4

12.3 g (0.05 mole) of γ-glycidyloxypropyltrimethoxysilane are added dropwise under nitrogen at 25° C. to 11.05 g (0.05 mole) of 4-amino-2,6-di-tert-butylphenol in 250 ml of ethanol. The reaction mixture is kept for 16 hours at reflux temperature, then cooled, and the solvent is evaporated, affording a viscous oil (23 g) having the following structure: ##STR26##

EXAMPLE 5

12.5 g (0.1 mole) of 2,4-dimethyl-6-aminophenol are dissolved in 150 ml of ethanol and then 23.6 g (0.1 mole) of γ-glycidyloxypropyltrimethoxysilane are slowly added dropwise to this solution. The reaction mixture is kept for 16 hours at reflux temperature. Working up as described in Example 4 yields 29.5 g of the following product: ##STR27##

EXAMPLE 6

A bomb tube is charged with 24.7 g (0.1 mole) of 4-allyl-2,6-di-tert-butylphenol, 12.1 g (0.1 mole) of trimethoxysilane and 0.5 g of hexachloroplatinic acid in 10 ml of isopropanol, and the mixture is heated under nitrogen to 180° C. The reaction mixture is cooled after 16 hours, the platinic acid filtered off, and the solvent evaporated. The residual viscous oil has the following structure: ##STR28##

EXAMPLE 7

9.82 g (0.05 mole) of mercaptopropyltrimethoxysilane and 13.2 g (0.05 mole) of N-dimethyl-4-hydroxy-3,5-di-tert-butylbenzylamide are dissolved in 50 ml of dimethyl formamide and the mixture is heated under nitrogen to 100° C. The reaction mixture is cooled after 16 hours and the solvent is evaporated (in a high vacuum, drying for 4 hours at 80° C.). The residue consists of 18.9 g of a clear red oil having the following structure: ##STR29##

EXAMPLE 8 Oil oxidation test, standard version in accordance with ASTM D 2272 (rotary bomb oxidation test)

A sample of Shell rotary vacuum oil (viscosity 11 cS/100° C.), to which 0.25 g of stabiliser has been added, is oxidised in a glass vessel in an oxygen atmosphere together with 5 ml of distilled water and a brightly polished copper spiral which has been washed with petroleum and which acts as catalyst. The glass vessel is in a bomb of stainless steel fitted with a pressure gauge. The bomb rotates axially at 100 rpm and at an angle of 30° to the horizontal in an oil bath at 150° C. The initial oxygen pressure before heating is about 6 atmos. (90 psi), rises at 150° C. to just on 14 atmos. (200 psi) and remains constant until the onset of oxidation. The test is complete at a fall in pressure of about 1.7 atmos. (25 psi). The time in minutes is recorded.

    ______________________________________                                                    Time in minutes until fall                                                     in pressure of about 25 psi                                         Stabiliser   Rot. Vac. P. Oil                                                  ______________________________________                                         without      57                                                                0.5% Nr. 1   185                                                               0.25% Nr. 7  80                                                                ______________________________________                                    

EXAMPLE 9 Oil Oxidation Test in Accordance with IP 280, "CIGRE" (modified, accelerated method IP 280)

Modified version with soluble Cu and Fe catalyst.

Conditions: introduction of oxygen over 4 hours at 150° C. (4 liters/O₂ /h).

Determination of the acid number after completion of test: consumption of KOH in mg per g of test oil (reported in table).

Test oil: Shell rotary vacuum oil (viscosity 11 cS/100° C.).

                  TABLE                                                            ______________________________________                                         Stabiliser     mg KOH/g                                                        ______________________________________                                         without        2.5                                                             0.5% Nr. 1     0.23                                                            0.25% Nr. 7    0.93                                                            ______________________________________                                    

EXAMPLE 10 TOST, oxidation characteristics of Vitrea 27 oil (ASTM D 943/DIN 51 587/IP 157)

The oil for testing is heated to 95° C. in the presence of water and an iron/copper catalyst, while measuring the time in hours in which the degree of neutralisation of the oil has reached a consumption of 2 mg of KOH/g (TOST life).

    ______________________________________                                         Stabiliser    TOST life in hours                                               ______________________________________                                         (0.25%) No. 1 1600                                                             none           100                                                             ______________________________________                                     

What is claimed is:
 1. A compound of the formula I ##STR30## wherein one of R₁ and R₃ is hydrogen and the other is OH, each of R₂, R₄ and R₅ independently is C₁ -C₁₂ alkyl, C₅ -C₇ cycloalkyl, C₆ -C₁₀ aryl or C₇ -C₉ aralkyl, and R₄ and R₅ are also hydrogen, R₆ is C₁ -C₁₈ alkyl, each of m and n independently is an integer from 0 to 6, X is the direct bond, --O--, --S--, --N(R₇)--, --Q--R₈ -- or ##STR31## wherein R₇ represents hydrogen, C₁ -C₁₂ alkyl, phenyl or a group of the formula II ##STR32## wherein R₁, R₂, R₃, R₄, R₅ and m are as defined above, Q is --O-- or --NH--, R₈ represents a group of the formula III

    --CH.sub.2 --CH(OR.sub.10)--CH.sub.2 --O--                 (III)

wherein R₁₀ is hydrogen, C₁ -C₁₂ alkyl or a group of the formula IV ##STR33## wherein r is an integer from 0 to 6, R₁₁ is hydrogen, C₁ -C₁₂ alkyl, C₅ -C₇ cycloalkyl, C₆ -C₁₀ aryl or C₇ -C₉ aralkyl, and R₉ is --O--, --NH--, --CH.H₂ N--, --O--CH₂ CH₂ --S--, ##STR34## --O--R₈ --, or a group of the formula V ##STR35## wherein R₈, R₁₁ and r are as defined above, and R₁₂ is C₁ -C₁₈ alkyl, C₅ -C₇ cycloalkyl, C₆ -C₁₀ aryl, C₇ -C₉ aralkyl or a group of the formulae VI or VII

    --(C.sub.u H.sub.2u)--COOR.sub.10                          (VI)

or ##STR36## wherein u is an integer from 1 to 6 and R₁₀, R₁₁ and r are as defined above.
 2. A compound according to claim 1 of formula I, wherein R₁ and R₅ are hydrogen and R₃ is OH.
 3. A compound according to claim 1 of formula I, wherein X is --N(R₇)--.
 4. A compound according to claim 1 of formula I, wherein m is 0 to 4 and n is
 3. 5. A compound according to claim 1 of formula I, wherein R₁ is hydrogen, R₃ is OH and each of R₂, R₄ and R₆ independently is C₁ -C₁₂ alkyl and R₄ is also hydrogen, R₅ is hydrogen or C₁ -C₆ alkyl, m is an integer from 0 to 4 and n is 3, X is the direct bond, --O--, --S--, --N(R₇)--, --O--R₈ -- or ##STR37## wherein R₇ is hydrogen or a group group of the formula II, in which R₁, R₂, R₃, R₄, R₅ and m are as defined above, Q is --O-- or --NH--, R₈ is a group of the formula III, wherein R₁₀ is hydrogen, C₁ -C₁₂ alkyl or a group of the formula VI, wherein r is an integer from 0 to 4, R₁₁ is C₁ -C₁₂ alkyl, and R₉ is --O--, --NH--, --OH.H₂ N--, --O--CH₂ --CH₂ --S--, --OR₈ -- or a group of the formula V, wherein R₈, r and R₁₁ have the above meanings.
 6. A compound according to claim 1 of formula I, wherein R₁ and R₅ are hydrogen, R₃ is OH, R₂ is C₁ -C₈ alkyl, R₄ is C₁ -C₄ alkyl, R₆ is methyl or ethyl, m is an integer from 0 to 4 and n is 3, X is the direct bond, --O--, --S--, --N(R₇)-- or ##STR38## wherein R₇ is a group of the formula II, in which R₁, R₂, R₃, R₄, R₅ and m are as defined above, R₉ is --NH--, --O--CH₂ --CH₂ --S-- or --OR₈ --, wherein R₈ is a group of the formula III, in which R₁₀ is hydrogen or a group of the formula IV, wherein R is 2 and R₁₁ is C₁ -C₄ alkyl.
 7. A compound according to claim 1 of formula I, wherein R₁ and R₅ are hydrogen, R₃ is OH, R₂ is methyl or tert-butyl, R₄ is tert-butyl, R₆ is methyl or ethyl, m is an integer from 1 to 3 and n is 3, X is the direct bond, --O--, --S--, --N(R₇)-- or ##STR39## wherein R₇ is a group of the formula II, in which R₁, R₂, R₃, R₄, R₅ and m have the above meanings, R₉ is --NH-- or --OR₈, wherein R₈ is a group of the formula III, in which R₁₀ is hydrogen.
 8. A compound according to claim 1 of formula I, wherein X is --NH--R₈ -- or ##STR40## in which R₈ is as defined in claim 8 and R₉ is --OH.H₂ N--.
 9. A compound according to claim 1 of the formula ##STR41##
 10. A lubricant additive containing a compound of the formula I according to claim
 1. 11. The use of a compound of the formula I according to claim 1 as a lubricant additive. 